fixed typo
removed unnecessary outspec
encapsulated node in/out mime types
some renaming and encapsulation
Refactored some parts of the code in preparation of a redesign of the GKN kernel.
Merge branch 'feature/code-improvements' into develop
improved output file node dialog. it now shows the available mime types,
respectively filters by valid extensions
generalized dialog and utilized it in OutputFiles as well
added warning dialog if wrong file type is selected
minor gui text changes
Fixed #74; implemented custom output file(s) dialog
Merge branch 'feature/file-restrictions-in-output-file-dialog' into develop